<===> input.scss
@function test($rest...,$param) {}
<===> error
Error: Invalid CSS after "...n test($rest...": expected ")", was ",$param) {}"
        on line 1 of input.scss
  Use --trace for backtrace.

<===> error-dart-sass
Error: expected ")".
  ,
1 | @function test($rest...,$param) {}
  |                        ^
  '
  input.scss 1:24  root stylesheet

<===> error-libsass
Error: required parameters must precede variable-length parameters
        on line 1 of input.scss
>> @function test($rest...,$param) {}
   ------------------------^